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U and V Node |
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U AND V NODESUV Mapping is the process that allows you to wrap a flat picture around a 3D object as a texture. It works by giving each point on the 3D mesh two extra coordinates. As well as the X, Y and Z coordinates that describe the 3D location of the point, each point on a UV mapped shape has a U and a V coordinate that control which part of the texture map that bit of the 3D object uses. The U coordinates work left to right, the V top to bottom, each running from 0 to 1 in Poser. UV Mapping is entirely arbitrary. Two identical 3D meshes can have totally different UV mapping, which directly affects the result of using the U and V nodes.UV MappingThe UV mapping of your object can have a massive impact on the results of a U or V based material. Figure 1 shows the standard Jessie textures as they appear in the material room. This picture will help us demonstrate several different features of U and V. First of all, more than one place on any figure can have the same UV coordinates. Here, U=0.5 V=0.5 is both the belly button on the body, and between the eyes on the head. This effect can be even more pronounced on an object with tiled UV mapping such as Poser's primitive cube prop. All six sides of the cube share the same UV mapping, so U=0.5, V=0.5 appears six times, once per face of the cube. Second, parts of your object that are close together on the model, or are very similar, can have very different U or V coordinates. Here, the hands and feet are on opposite sides of the map, so the left hand has high U values and the right hand low ones (for some reason the right hand is mapped on the left side of the texture!). The mapping here is relatively sensible, so things only differ in either U or V, but there is no reason why one hand couldn't be at the top right and the other at the bottom right, giving the two hands completely different UV coordinates. Third, the U and V coordinates can start again from zero or jump randomly across your model. Figure 2 shows that happening to the U coordinates as they cross the shoulders. The V coordinates are just as dramatic, starting from zero at the base of the neck. Fourth, like all texture maps, the UV coordinates produce seams. Figure 2 shows the seams on the back of Jessie, running clearly up the back of the body and the head, with a break for the shoulders. This doesn't mean that you can't use U or V to give you positions on a model. Plenty of models have UV mapping that can be used directly without any odd jumps or sudden changes of pattern. The Poser primitives are perfect for this - V provides a perfect high variable up the cube, cylinder or sphere primitives. Secondly, the leaps and breaks in the UV mapping often come at the edges of materials. In the Jessie map, the main breaks in the V coordinates come when the material changes from body to head, so you can modify one or the other material to take this break into account. The most effective use of the U and V coordinates is often to use them as indicators of direction, used to produce stripes or bars. Figure 4 shows the V mapping on the Jessie buisness suit. Displayed like this, the main part of the suit has smooth mapping, but the sleeves do not, being much darker than the rest of the suit. Worse, the left arm is mapped above the right, so is slightly lighter. However, figure 4 shows a stripped material created by passing the V coordinate through a Floor node then a Mod node (more on this later). The U and V nodes are at their most powerfull when combined with each other and with maths nodes. They can produce fades, stripes, ridges and even circles! |
